This invention relates to a magnetic disc apparatus and, more particularly, to a magnetic disc apparatus including a plurality of magnetic recording heads for magnetic recording and reproducing on a plurality of tracks formed on the magnetic disc.
FIG. 1 illustrates an example of a conventional magnetic disc apparatus which is disclosed in U.S. Pat. No. 4,307,425.
The conventional magnetic disc apparatus comprises a magnetic disc drive assembly 20 mounted on a base (not shown) and a magnetic head supporting assembly 30 disposed on the base in a predetermined positional relationship with respect to the magnetic disc drive assembly 20.
The magnetic disc drive assembly 20 comprises a rotary shaft 21 for supporting a magnetic disc 23 and a motor 22 for rotatably driving the rotary shaft 21.
The magnetic head supporting assembly 30 comprises a rotary actuator 31 including a rotary shaft 32 which is pivotably mounted on the actuator 31 and an actuator arm 33 which is secured to the rotary shaft 32. The actuator arm 33 has a pair of mounting members 34, each extending from one end of the actuator arm 33. The head supporting assembly 30 further comprises a pair of suspension arms 35, each inwardly extending from one side of the mounting member 34 of the actuator arm 33. Each suspension arm 35 resiliently supports at the extending end thereof a magnetic head 36a or 36b by which magnetic recording and reproducing are achieved on the disc 23. The actuator arm 33 is swingably driven about the rotary shaft 32 by the rotary actuator 31 to move the suspension arms 35 in parallel with the disc surface thereby positioning each of the magnetic heads 36a and 36b at a desired position over the magnetic disc 23.
Now, the disc 23 has coaxial outer and inner tracks T1 and T2 formed on the surface thereof and data is stored on these tracks. Accordingly, the magnetic head 36a accesses the outer track T1 and the magnetic head 36b accesses the inner track T2. When mounting the magnetic heads 36a and 36b in a predetermined positional relationship relative to the tracks, for instance, the head 36a is first moved to an accurate position relative to the outer track T1 and on the basis of the accurate position of the head 36a, the head 36b is adjusted to a position relative to the inner track T2.
Accordingly, only the outer track T1 has tracking servo-information stored thereon and on the basis of the servo-position for the head 36a, i.e. reference moving position, the head 36b is adjusted to a position relative to the inner track T2.
The mounting angle of each of the magnetic heads 36a and 36b is determined in such a manner that the deviation angle of the heads 36a and 36b is smallest with respect to the respective tracks formed in the radial direction of the disc 23, when the actuator arm 33 is swung.
The thus-constructed conventional disc apparatus has problems in that the length of the suspension arms 35 is limited in comparison to the fact that the actuator arm 33 can be made longer, and it becomes difficult to mount a magnetic head lifting mechanism or the like for each of the suspension arms, whereby restrictions in the layout of the components arise. If a plurality of magnetic heads are provided on the actuator arm for accelerating the access time, the distance between one head which is used as a reference and the other head disposed at a predetermined distance with respect to the reference head varies as a function of changes in temperature and the distance between the tracks on the disc surface also varies as a function of changes in temperature. In order to make these varying distances as identical as possible to each other, the disc and the magnetic heads must be made of a material having the same coefficient of expansion, such as aluminium, resulting in a high cost apparatus.